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At least 739 records · Page 41Linked to original sources
PubMed1995

[Reduction of induced corneal astigmatism after IOL implantation by small incision technique].

PURPOSE: To investigate the effect of incision length on corneal astigmatism after intraocular lens implantation. METHODS: The change of induced corneal astigmatism was observed in 36 patients underwent phacoemusification cataract extraction with intraocular lens implantation through a 6.5 mm limbal incision comparing with that in extracapsular cataract extraction with intraocular lens implantation through a 11 mm limbal incision. RESULTS: The surgically induced astigmatism in 1 week, 1.3 and 6 months after the operation was 2.13 +/- 1.41, 1.58 +/- 1.07, 0.92 +/- 0.75 and 0.77 +/- 0.55D in 6.5 mm limbal incision group while that was 4.63 +/- 1.39, 3.08 +/- 1.11, 2.52 +/- 0.89 and 2.04 +/- 0.87 in 11 mm incision group, the difference in the same postoperative period was significant (P < 0.05). At 1 week and 1 month postoperatively, 52.8% and 61.41% of 6.5 mm limbal incision cases had uncorrected visual acuity of 0.5 or better compared with 28.6% and 37.1% of 11 mm incision cases (P < 0.05). There was no difference of the uncorrected visual acuity 6 months after the surgery between the two groups. CONCLUSION: Reducing incision can minimize surgically induced astigmatism and promote early postoperative visual rehabilitation.

Aged↗
PubMed1996

[Corneal astigmatism after tunnel incision for cataract extraction].

PURPOSE: To evaluate the development of astigmatism after cataract extraction depending on the kind of incision MATERIAL AND METHODS: Astigmatism was examined in 107 eyes of 92 patients, who underwent cataract extraction, mostly with IOL's implantation. In 52 eyes phacoemulsification with tunnel incision, measuring 5 mm in 27 and 8 mm in 25, was performed. In the control group of 55 eyes incision with scleral flap measured 2/5 of the corneal circumference. In cases with 5 mm incisions no sutures were used, in 8 mm incisions wounds were closed with single sutures and in control group the double continuous sutures were applied. Astigmatism was measured in two days, one week, four weeks and 3 months after surgery. RESULTS: Post-operative astigmatism decreased gradually and after 3 months was average 0.14 D in the eyes without sutures, 0.68 D in those with single ones and 1.78 D in the control group.

Adolescent↗
PubMed1997

Photorefractive keratectomy for the treatment of compound myopic astigmatism using the ablatable mask.

Eight eyes of 8 patients with compound myopic astigmatism were treated with excimer laser photorefractive keratectomy (PRK) using a hand-held ablatable mask in conjunction with the Summit excimer laser. The attempted correction ranged from -1.25 to -400 dioptres (D) of astigmatism and 0 to -8.00 D of myopia. All eyes had attained at least 6 months of postoperative follow-up. Five of the 8 eyes achieved an unaided visual acuity of 6/12 or better. Postoperative refractions ranged from -0.50 to -3.50 D of refractive cylinder and from +0.50 to -3.75 D of spherical error. Decentration of the ablation zone was encountered in 3 eyes due to shifts in patients' fixation. Technical difficulty with the use of the hand-held ablatable mask limited the widespread application of this procedure and it has now been superseded by newer excimer laser systems which can correct astigmatism without having to employ a mask. Despite this, because of the theoretical ability of the mask to correct any form of refractive error, the concept of the mask shape transfer process will remain as a potential alternative in refractive surgery, especially for correction of hyperopia and hyperopic astigmatism.

Adult↗
PubMed1997

[How to correct astigmatism?].

The total astigmatism is measured by an automatic refractor. The astigmatism is corrected by a cylindric lens. For children cycloplegia is required. For children below school age an astigmatism is corrected only if it exceeds 2d. Children older than 6 years will benefit from correction of astigmatism if this is more than 1d. Prescription will be progressive to be supported.

Adult↗
PubMed1997

[Corneal astigmatism after trabeculectomy].

PURPOSE: The aim of the present study was to investigate the effect of conventional and mitomycin trabeculectomy on the corneal astigmatism. SUBJECT AND METHODS: Measurements with the use of computer-assisted videokeratography (Eye-Sys) were performed in 34 glaucoma patients who underwent trabeculectomy. Color-coded topography maps were analyzed to obtain astigmatic data. RESULTS: The mean surgically-induced astigmatism in conventional trabeculectomy group was 2.2 D and in the mitomycin group 4.0 D, 1 day post-op, 1.3 D and 3.0 D after 10 days and 0.4 D and 1.1 D after 3 months, respectively. CONCLUSION: There was an apparent correlation between the amount of induced astigmatism and the use of mitomycin. This may be related to the impaired healing process of trabeculectomy wound and lower intraocular pressure in the mitomycin group.

Astigmatism↗
PubMed1998

[Evaluation of astigmatism and blood-aqueous barrier breakdown following procedures in the anterior eye segment].

PURPOSE: The aim of this study was to evaluate the disruption of the blood-aqueous barrier (BAB) and the induced astigmatism following phacoemulsification, trabeculectomy and phacotrabeculectomy. MATERIAL AND METHODS: 141 eyes of patients who underwent different surgical procedures of the anterior segment were examined with the use of computer-assisted videokeratography. All maps were recorded preoperatively, and one and five days after surgery. We also applied a laser flare-meter in 41 eyes in order to quantify aqueous flare following these procedures. RESULTS: The mean surgically-induced astigmatism following conventional trabeculectomy was 2.1 D and 1.4 D one and five days postoperatively, phacoemulsification with sutures 2.7 D and 1.9 D and phacotrabeculectomy 3.0 D and 2.4 D, respectively. Lower values of astigmatism obtained after sutureless phacoemulsification were 0.6 D and 0.3 D one and five days postoperatively, respectively (p < 0.05 vs Phaco+IOL+Trab. group, p < 0.01 vs other groups). It was found that aqueous flare values following phacotrabeculectomy were 58.0 photon counts/milisec.--one day, 39.3--3 days, 24.4--7 days, 20.4--10 days postoperatively. Significantly reduced values were observed after phacoemulsification--27.6 one day after surgery and 17.6--3 days later (p < 0.01 vs Phaco+IOL+Trab.group). CONCLUSIONS: It could be concluded that induced astigmatism and the amount of inflammation were the highest after triple procedure and the lowest after phacoemulsification.

Anterior Chamber↗
PubMed1998

Astigmatic changes after sutureless small-incision cataract-surgery using a superior or temporal corneal incision.

The main purpose of this study is to compare the difference in surgically induced astigmatism and stability in sutureless small-incision cataract-surgery with a superior or a temporal approach. Using the Cravy- Jaffe- and Naeser-method for calculating surgically induced astigmatism, we evaluated astigmatic changes in eyes that underwent sutureless small-incision cataract surgery via the superior (66 eyes of 65 patients) or the temporal (39 eyes of 39 patients) approach. In the early postoperative period, our calculations showed a typical against the rule-shift in the corneal superior group, while the corneal temporal group showed a slight with-the-rule shift. The temporal approach proved to be more stable and provoked less induced astigmatism than the superior approach.

Astigmatism↗
PubMed2006

Determination of astigmatism in TEM images.

We have developed a new two-step algorithm to determine the astigmatism of images from transmission electron microscopes (TEMs). Instead of computing the radial average of the power spectrum, we divide the power spectrum of a TEM image 1 to m (typically 32) sectors. We use a technique based on perturbation analysis of the contrast transfer function (CTF) to assimilate sector averages of the power spectrum of an image, which are incoherent in the presence of astigmatism, to a coherent radial average corresponding to a nominal defocus value. This is based on the fact that small defocus change from a nominal value can be considered to be equivalent to a perturbation on the spatial frequency spectra. Thus, instead of measuring the angular defocus variations, we optimise the frequency change required to obtain a coherent radial average. Numerically, this is achieved by minimizing sigma(2)/sigma(1) of a matrix formed from the sector averages, where sigma(i) denotes the ith singular value of the matrix. After the minimisation procedure, the second singular value should be very small compared with the first singular value, indicating that the matrix is nearly rank unity. In the second step, the nominal defocus can be obtained from the coherent radial average using any good defocus estimation program, which assumes zero astigmatism. The defocus value at a sector can be obtained from this nominal defocus value and one of the parameters from the unconstrained optima. Our algorithm is tested on astigmatic images of carbon film, 2D crystals of bacteriorhodopsin and cryo-images of HIV cores.

Algorithms↗
PubMed2001

Vision of low astigmats through thick and thin lathe-cut soft contact lenses.

Distance and near visual acuity of 13 low astigmats were determined in a double-masked experiment through thick and thin (centre thickness 0.12 mm and 0.06 mm, respectively) spherical lathe-cut soft lenses. For each lens type, distance and near LogMAR VA and over-refraction were assessed with different logMAR VA charts. For 70% of the subjects, the residual astigmatism was significantly lower than the refractive astigmatism with thicker lenses. No statistically significant differences in the distance and near logMAR VA was found between the two lens types using any of the charts used, though, in general, logMAR VA obtained through the thicker lens was better than logMAR VA through the thinner lens. The variabilities in distance and near logMAR VA between the two lens types increased with decreased contrast. The variabilities in distance logMAR VA were greater with Chinese charts than with English charts, and LogMAR VA with Chinese charts were significantly worse for both lens types. Based on the results of this study, we concluded that thicker spherical lathe-cut soft lenses provide better vision in low astigmats. The Snellen acuity test is inadequate for vision assessment of soft contact lens wearers. When a patient wearing thin soft contact lenses complains of poor vision in spite of 6/6 or 6/5 Snellen acuity, changing to thicker lenses may be considered.

Journal Article↗
PubMed2005

Limbal relaxing incisions versus on-axis incisions to reduce corneal astigmatism at the time of cataract surgery.

PURPOSE: To compare limbal relaxing incisions (LRIs) with placement of the corneal cataract incision on the steepest keratometric axis for the reduction of preexisting corneal astigmatism at the time of cataract surgery. SETTING: The Queen Elizabeth Hospital, Adelaide, South Australia, Australia. METHODS: In a prospective single center study, patients having 1.5 diopters (D) or more of keratometric astigmatism were randomly assigned to 2 surgical techniques: on-axis incisions (OAIs) consisting of a single clear corneal cataract incision centered on the steepest corneal meridian or LRIs consisting of 2 arcuate incisions straddling the steepest corneal meridian and a temporal clear corneal incision. Vector analysis of the target axis flattening effect was used to assess the efficacy of treatment. RESULTS: Seventy-one eyes of 71 patients were evaluated, 33 in the OAI group and 38 in the LRI group. Six weeks postoperatively, the flattening effect was 0.41 D (median and interquartile range 0.15 to 0.78 D) in the OAI group and 1.21 D (range 0.43 to 2.25 D) in the LRI group (P = .002). After 6 months, the flattening effect was 0.35 D (range 0.00 to 0.96 D) and 1.10 D (range 0.25 to 1.79 D), respectively (P = .004). CONCLUSION: The amount of astigmatism reduction achieved at the intended meridian was significantly more favorable with the LRI technique, which remained consistent throughout the follow-up period.

Aged↗
PubMed1987

Refractive keratoplasty for disabling astigmatism after penetrating keratoplasty.

Postoperative astigmatism is one of the major limitations of penetrating keratoplasty. In an attempt to reduce postkeratoplasty astigmatism, we combined corneal-relaxing incisions with orthogonal compression sutures, guided by the intraoperative use of a ring keratometer. Eleven consecutive patients from a mixed referral population with functionally disabling astigmatism were studied. The average preoperative keratometric cylinder of 11.68 diopters was reduced by 7.95 (+/- 3.03 SD) diopters. Each patient's net keratometric cylinder was reduced. We believe that this technique is safer and more predictable than previously published techniques.

Astigmatism↗
PubMed1988

Paired arcuate keratotomy. A surgical approach to mixed and myopic astigmatism.

Twenty-five cadaver eyes were used to study the effect of paired arcuate keratotomy on corneal astigmatic changes. Paired arcuate incisions placed at optical zones of 5, 6, 7, 8, and 9 mm were progressively lengthened from 45 degrees to 60 degrees, 90 degrees, and, finally, 120 degrees. The corneal flattening in the meridian centered over the incisions and the corneal steepening 90 degrees away were quantified with each successive lengthening. Linear regression analysis showed a direct linear relationship of corneal astigmatic change (sum of corneal flattening and steepening, or delta K) to decreasing optical zone size as measured in millimeters and increasing incision length as measured in degrees. The delta K value ranged from 2.65 +/- 1.07 diopters to 22.05 +/- 3.55 D. The flattening/steepening coupling ratio mean was 1.47 +/- 0.41. Progressively longer paired arcuate incisions produced a predictable and titratable corneal flattening in the meridian centered over the incisions and a slightly smaller corneal steepening 90 degrees away, making the procedure ideal for mixed astigmatism.

Anthropometry↗
PubMed1989

Corneal astigmatism after cataract surgery.

206 Consecutive cataract patients were at random divided into three groups according to the way the cataract incision was closed: virgin silk 8-0, interrupted nylon 9-0, and double running nylon 9-0. The nylon, whether interrupted or continuous, yielded in the majority of cases a postoperative astigmatism with the rule, whereas virgin silk caused in nearly all patients a postoperative astigmatism against the rule and therefore behaved like an absorbable suture. Silk is chemically non-absorbable, but in virgin silk a natural worm-produced polymer is still present, which provokes a tissue reaction. Softening of tissue diminishes the tensile strength of the suture. With respect to the postoperative astigmatism, the suture material (nylon or virgin silk) seems a more important factor than the way in which it is used (interrupted or continuous).

Aged↗
PubMed1994

Influence of suction cup oculopression on corneal astigmatism.

In 11 (right) eyes of 11 ocularly healthy subjects an artificial stepwise intraocular pressure (IOP) elevation was applied by suction cup oculopression. The initial negative pressure in the suction cup was 80 mmHg; it was raised in steps of 40 mmHg. The median of the corneal astigmatism, measured with a Zeiss ophthalmometer, was 0.50 D before oculopression (the values of the 10th and 90th percentiles were 0.30 and 1.10 D, respectively). Corneal astigmatism increased to 2.00 (0.00-5.10) D, 2.25 (1.00-5.55) D, 2.63 (0.63-7.00) D, 3.38 (1.88-6.88) D, 3.38 (2.83-7.25) D, and 4.38 (2.85-5.63) D with 80, 120, 160, 200, 240, and 280 mmHg oculopression, respectively. The astigmatism dropped to 0.75 (0.00-2.30) D immediately after removal of the suction cup. Thus, suction cup oculopression not only influenced IOP but also ocular refraction. This is of particular importance since visual evoked potential (VEP) amplitude is to a high degree dependent on refractive changes. This fact has to be considered if changes in VEP amplitude during suction cup oculopression are used as a tolerance test in glaucoma diagnosis.

Adult↗
PubMed1980

[Preoperative Placido photography in keratoconus and its meaning in conjunction with postoperative astigmatism (author's transl)].

The preoperative shape of an eye affected by keratoconus can be evaluated by means of Placido photography of the cornea and the "Placido axis" of the main astigmatic error determined (Figs. 1, 2). In 64% of 105 cases it was shown that the postoperative astigmatism correlated well with the preoperative Placido axis (Table 5). A perfectly circular graft if transplanted, will therefore again adopt the preoperative shape of the cornea. From the facts above, a slightly oval graft sutured perpendicularly to the preoperative main Placido axis would probably compensate for this astigmatism but this has not been carried out experimentally as yet.

Adult↗
PubMed1976

[The astigmatism bioblique. II. Mathematical description (author's transl)].

Optical surface showing an astigmatism bioblique could only approximately be described by mathematical formulas. The best approximation is that one which shows a close relation between regular and bioblique astigmatism. It allows the calculation of the best correcting cylinder, which brings the anavoidable residual astigmatism to a minimum.

Astigmatism↗
PubMed1995

Astigmatism and visual recovery after phacoemulsification and conventional extracapsular cataract extraction.

In this study we wanted to investigate the post-operative astigmatism and visual acuity after phacoemulsification and conventional extracapsular cataract surgery. Patients operated between April and June 1993 (n = 150) were retrospectively analyzed. The patients were examined prior to surgery and at day 1, at day 10, and in week 6 post-operatively. The difference between the post-operative log mean visual acuity in the Phaco group and in the CECCE group was significant after 1 and 10 days, however it was not significant (p = 0.191) after 6 weeks. The mean astigmatism was significantly less in the Phaco group than in the CECCE group during the whole post-operative check-up period. This study suggests that Phaco results in a lower post-operative astigmatism and an earlier visual rehabilitation compared to the CECCE technique.

Astigmatism↗
PubMed1977

Surgical induction of corneal astigmatism. An experimental study.

The aim of all ocular surgery is to preserve or restore optimal visual function. Reduction of excessive postoperative astigmatism after keratoplasty, cataract extraction, or other anterior segment operations has been obtained in clinical surgery by corneal wedge resection. The purpose of this experimental investigation was to quantify and evaluate the results of different microsurgical techniques in crescentic resection of a corneal wedge. Twenty-five rabbits were operated and the induced changes of corneal curvature measured by keratometry. The immediate and long-term results are presented. The effect of wedge resection was a steepening of the meridian perpendicular to the resection and a flattening of the meridian parallel to the resection. The astigmatism induced was less pronounced than the changes obtained in human surgery. There were no postoperative ocular complications and all corneas remained clear. It is suggested that the operation be performed in all cases of severe corneal astigmatism uncorrected by lenses.

Animals↗